BEIRUT - China threw its weight behind United Nations (UN) envoy Kofi Annan on Wednesday, backing his call to include Iran in internationally-brokered talks to resolve Syria's crisis - in the face of strong Western opposition.

"China believes that the appropriate resolution of the Syria issue cannot be separated from the countries in the region, especially the support and participation of those countries that are influential on relevant sides in Syria," Foreign Ministry spokesperson Liu Weimin said in Beijing.

UN Security Council veto-holders China and Russia have for the past year blocked efforts by Washington and its European and Gulf Arab allies to turn the screws on Syrian President Bashar al-Assad, fighting to defend his mostly Alawite ruling establishment against an uprising dominated by Sunni Muslims.

Assad's opponents say just under 13,000 armed and unarmed opponents of Assad, and around 4,300 members of security forces loyal to Damascus, have been killed since he launched a crackdown 16 months ago, using tanks and helicopter gunships to attack rebel strongholds inside Syria's biggest cities.

Activists on Wednesday reported a new bombardment of rebel areas of Homs, a hotbed of opposition to Assad, as well as fighting in many other parts of the country.

Annan was due to brief the Security Council at 4:30 pm British time on Wednesday on the results of a lightning diplomatic shuttle this week to Damascus, Tehran and Baghdad - three capitals forming a Shi'ite Muslim axis of power in the Middle East.

Annan plunged into a tussle between the major powers on Tuesday, insisting that Iran, which strongly backs Assad and is regarded as an adversary of the West and Gulf Arabs, had a role to play in the drive to relaunch stalled peace efforts and begin talks towards a political transition.

In Baghdad, Annan also won backing from Iraqi Prime Minister Nouri al-Maliki, who like Assad has close ties to Tehran.

Washington's reaction was not encouraging for the envoy.

"I don't think anybody with a straight face could argue that Iran has had a positive impact on developments in Syria," White House spokesperson Jay Carney told reporters.